This invention relates generally to permanent magnet motors and more particularly, to magnet arcs for magnet motors and a method of assembling the magnet arc to a rotor.
Permanent magnet motors, also known as electronically commutated motors (ECM's), are used, or have potential for use, in a wide variety of applications, such as alternators, electronic throttle controls, electric power steering, fuel pumps, heater and air conditioner blower motors, and engine cooling fans. Typical permanent magnet motors have a plurality of arcuate-shaped magnets affixed about the core or circumference of a rotor. The rotor is positioned inside a closely-fitting housing which carries electromagnets for propelling the rotor shaft.
These magnet arcs are affixed to the rotor core using an adhesive. Typically, three such magnet arcs are used, which have an inner curvature that circumscribes the outer circumference of the rotor core. It is desired to have a tight fit or bond between the inner face of the magnet arc and the rotor core to provide a durable and efficient motor. These magnet arcs have straight sides that are parallel to the longitudinal axis of the rotor. Prior magnet arcs have manufacturing tolerances that must be accounted for in assembling the arcs to the rotor core. To ensure that a tight fit between the inner face of the magnet arc and the outer circumference of the rotor core will be achieved, gaps occur between the magnet arcs. These gaps have a negative impact on the operation and performance of the permanent magnet motor, including resulting anomalies in the flux. Additionally, a gap formed between the magnet arcs, or a skewed line between the arcs, which passes by the teeth of the stator provides a blade pass component to the noise and torque of the motor. In prior motors, the total combined degree of curvature of the magnet arcs is less than 360 degrees.
For example, based upon an industry tolerance of +/−1 degree of curvature in the manufacture of magnet arcs, three magnet arcs of 118.5 degrees can be used in the assembly of the magnet motor. Nominally, there will be gaps between the magnet arcs of 1.5 degrees each. With the maximum positive tolerance occurring during manufacturing, there will be gaps of 0.5 degrees between each magnet arc but with the maximum negative tolerance occurring during manufacturing, there will be gaps of 2.5 degrees between each magnet arc. The typical method of assembly uses application of a radial force each of the magnet arcs and attempts to evenly distribute the gaps between the magnet arcs.
Accordingly, there is a need for a magnet motor with magnet arcs that address one or more of the aforementioned drawbacks and of the prior art. In addition, there is a need for a method of assembly of a permanent magnet motor that minimizes the gaps between the magnet arcs that are affixed to the rotor core.